I'm not going to bore you with an intro, here are ways to know he's the right guy.
1) He cares about what you care about, a lot
There's something very special about a guy that cares about what interests you. You want him to be the guy that never misses your soccer game or encourages your music dream or pushes you to go after whatever your dreams are. He cares.
2) You can communicate with eye contact
When you're with a group of people and someone says something stupid or funny, who do you look to? The right guy is the one you can give one look too and they know exactly what you're feeling.
3) He's probably more concered about your health and safety than you are
He's the guy that panics if you bump your head too hard or slip down the stairs (And he's also the guy that laughs when he knows you're okay). He's the guy that takes the food out of the oven every time so you don't burn yourself. And he's the guy that makes sure you're not drinking too much (unless you're trying to out-drink each other, then game on)
4) He respects you like a best friend
You're his best friend, and he's yours.
5) He didn't push for sex, it happened when it happened, when both of you were ready
It wasn't something he tried to convince you to do or made you feel guilty for not doing, it was something you both wanted. Or maybe you're not ready yet, he doesn't mind.
So here are just a few things, hope it was helpful :)